Telephone system



E. P. G. WRIGHT ET AL TELEPHONE SYSTEM Filed Sept. 26, 1934 '7 Sheets-Sheet 1 ER 6. WRIGHT lNVENTORS': 6.C.HARTLEV WJREYNOLDS ATTORNEY E. P. G. WRIGHT ET AL TELEPHONE SYSTEM 2 t vat Nut h w 52k EUR 3 8m t W 56K QR S 7 5st Ex I \U 4 29. w. 3 I 9 I l 6 2 t w Lw -Lw 15 d e l .1 F

m: IIIR IIIDU |D U 0% 3 6D INVENTORS 6.6.HAR7'LEV WJRE'VIVOLDS ATTORNEY Dec; 1935- E. P. G. WRIGHT ET AL. 2,

TELEPHONE SYSTEM Filed Sept. 26, 1954 7 Sheets-Sheet 5 E'.P.G. WRIGHT //VVENTOR$ G.C.HARTL'Y 1 By MCJREVNOLDS ATTORNE V E. P. G. WRIGHT ET AL.

TELEPHONE SYSTEM Nud- 90m mvm 7 Sheets-Sheet 4 IN VE N TOPS unnfl isluiiirlll UUDHT lilvllllllllfl.

Filed Sept. 26, 1934 EDGE lllllllllll k V ATTORNEY Dec. 24, 1935.

E. P. G. WRIGHT ET AL TELEPHONE SYSTEM Filed Sept. .26, 1934 7 Sheets-Sheet 5 ERG w GHT 6.6. HARTLEY By W.J.REYNOLDS 95% I IN !/E N TOPS DUUMMMMMHMMMMWD M. M

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EUEEEEL UDDDDDL ATTORNEY Dec. 24, 1935.

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E. P. G. WRIGHT ET AL 2,025,408

TELEPHONE SYSTEM Filed Spt. 26, 1954 :31" lHl' 7 Sheets-Sheet 6 LOOP DIAL/N6 TRUNK bro-war fnwvx rq MAIN OPERATOR "0' CALL lNVENTORS G.G.l-IARTLY W.J.REYNOLD$ BY A TTORNE Y 24, 1935. E. P. G. WRIGHT ET AL 2,025,408

TELEPHONE SYSTEM Filed Sept. 26, 1954 7 Shets-Sheet 7 TO AUTOMA T/C I} E k 1 FIG. 6

TWO WAY TRUNK WI 7' H BA 7' FER? DIAL 1N6 ERRWRIGHT G.C.HARTL'Y WJ. REYNOLDS v gm ATTORNEY lNVE/VTORS Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Application September 26, 1934, Serial No. 745,490 In Great Britain October 6, 1933 12 Claims.

This invention relates to automatic orsemiautomatic telephone exchange systems and more particularly, although not exclusively, to small exchanges for use in rural areas.

One object of the invention is to supply alternative trunking facilities without the use of registering mechanisms.

It is desirable to avoid the use of a plurality of registering mechanisms on rural boards and therefore it is proposed to reach an adjacent board on an alternate trunking basis by the use of a link circuit which, in response to the first digit of a two-digit number designating said adjacent board, selects a tie-line to the said board and absorbs the second digit. If, on the other hand, no tie-line is available, the link, in response to the first digit, selects a trunk to the main office where the connection to the required board is then made in response to the second digit.

Another object of the invention is to allow coin-box subscribers to have speech connection with a number of other exchanges by dialing a single digit and without payment. Some Well known coin-box lines do not allow speech without payment unless the single digit is dialed. With a known. design of'rural board, the operator can only be reached by dialing two digits, such as 01, and consequently arrangements have been made tomodify the coin box. According to the present invention, the operator is reached by dialing the single digit 0 and therefore the standard coin box will be used. Difficulty arises in cases where access is obtained to other manual exchanges by dialing other single digits because it is necessary for money to be inserted before speech can commence with the operator who does not guarantee the required connection. We propose to arrange the switching mechanism so that manual exchanges may be obtained by dialing a high digit initially, whereas automatic connections are only completed with an initial digit below 7, in which case it is necessary to insert coins.

A further object of the invention is to provide access over a trunk either direct to a manual board or direct to automatic equipment. The exchange equipment is, therefore, arranged so that, by dialing different digits or combinations of digits, the same trunk or trunk group is seized and thereafter a discriminating signal is sent over the trunk to extend the connection either to the manual board or to the automatic equipment.

Another object of the invention is to provide recall facilities for a subscriber who finds a wanted connection unavailable. The particular atrangement proposed is that recall facilities are provided for trunk calls to a manual board. When this facility is required on a trunkgiving access either to a manual board or to automatic equipment, the link is arranged to discriminate between the two types of calls and on the dialing of a recall digit to give recall facilities on calls to the manual board only if a trunk extending thereto is not available at the time. The subscriber is then rung when a trunk becomes free, the trunk is seized and the operator is signaled.

Another object of the invention is to provide iacilitiesfor extending connections to areas designated by different numbering systems, as, for instance, a connection between a three-digit local board and a four-digit main exchange area. In such a case, the rural subscribers are given four digit numbers, the link absorbing the, first digit in setting up a local connection and using it in setting up an interoffice connection.

Yet another object of the invention relates to multi-metering. The link, which is the subject 25.

of this invention, may be arranged either for multi-metering or single metering. The multimetering arrangement is such that tariff discrimination may take place in response not only to one digit but also in response to two, three and more digits, the equipment being capable of modification to discriminate after additional digits also if required.

Other objects of the invention relate to coinbox facilities. Excess fee calls from coin boxes may be connected to an operator at the main exchange or to N. U. tone without extra cost. An extra wiper on the finder switches is used for coin-box discrimination and for discrimination between other diiierent types of incoming 40 calls, and for calls between two similar rural boards, forming in effect one exchange, when the terminating board must be arranged to receive a digit less than usual. Coin-box discrimination can be also provided on tie lines.

Another object of the invention is to provide centralized testing facilities for testing equip ment at one exchange from the centralized testing facilities. In the preferred embodiment, one trunk is provided for access and hold purposes and a second junction for testing subscribers lines, these being connected to finder banks and to final selector wipers, respectively. The final selector may be stepped from line to line from the distant exchange. 55,

The nature of the invention will be more clearly understood from the following description of one embodiment thereof and of possible modification thereto with reference to the accompanying drawings in which:

Fig. 1A shows a subscribers line and trunk circuits terminating on the banks of the line finder I20 which is a part of the link shown in Figs. 1 to 4, inclusive;

Figs. 1 to l, arranged as shown in Fig. 1B, show the link circuit having a line finder I20, a line and trunk connector 3I0 and a registering mechanism 410;

Figs. 5 and 6' show the various trunks which may be used both outgoing from connector 3I0 and incoming to the finder I20 for connections outgoing from or incoming to the local office in which said link is located. While these trunks are typically representative ofthe possible kinds of extensions and are shown, for purposes of illustration, extending more or less indiscriminately' from the banks of connector 3I0, it is obvious that, if desired, only one group of each may be used to the exclusion of the other for any particular digit or group of digits marking a trunk group; and

Fig. 7 shows, in diagrammatic form, the equipment of two associated one hundred line boards.

Referring first to Fig. '1, up to one hundred subscribers PI and both way trunk and tie line circuits JC and TC can be connected to the banks of the finders I20 and connectors 3I0 of a group of link circuits LCI having marker or pilot switches M0, and form a rural board. Two such boards, comprising links LCI and LC2, respectively, may be connected together as shown by tie lines comprising both way circuits TC. A number of groups of junctions may be connected to the boards. The switches 3 I 0, 3 I 0 have access to recall circuits RCI, RC2 which are last choice 7 in the group of outgoing trunks to a main exconductor I I4.

change when seized'to give accessto an operator. By dialing a further digit when a recall circuit is seized, the link circuit and recall circuit are locked up, the calling party can restore so that, when a trunk becomes free, the calling party will be rung and the trunk seized.

A number of different types of call will now be described with reference to all the figures which show the detailed circuit arrangement.

Local call When the local subscriber I00 initiates a call, line relay I33 operates over a circuit extending from battery through the right winding of said relay, right outer back contacts of cut-off relay I32, subscribers loop to ground on the right inner contacts of relay I32. Relay I33 operates, connects battery potential through the left and right windings, respectively, of relays I32 and I33 and resistance 1 34 to the S conductor to guard against the-seizure of the line, and connects ground through its left inner contacts and the left inner back contacts of relay I32 to the common start A circuit for relay 305 is thereby completed extending from ground on said conductor, lower winding of relay 305, conductor 342, No. 2 contacts of relay I I0, conductor I31, brush 3 I4 and first terminal of its bank in switch 3"], conductor 343, terminal and brush 406 of register switch 4I0, interrupter contacts of switch magnet 40I, winding of said magnet to battery. Relay 305 operates but magnet 40I does not and on operating closes a self-interrupting circuit for magnet H3 ofline finder-I20 extending from ground on the upper No. 1 contacts of relay 305, conductor 344, normal contact and brush H6, conductor I38, lower No. 3 contact-set of relay 30I, conductor I43, upper back contacts of relay I04, lo'wer No. 4 back contacts of relay H5, interrupter contacts of magnet I I3 to battery. The switch brushes are now driven in search of the calling line, the circuit for magnet II3 through brush I I6 being completed to ground on bank I I1 after the brush has advanced beyond the normal 10 terminal.

The calling line is designated by the presence of battery through the right inner contacts and left winding of relay I33 and right winding of cut-oil relay I32 on its representative terminal 15 on bank I I8 so that when brush I I0 engages said terminal, a circuit for relay I04 is completed extending from battery as traced to brush I I9, conductor I30, lower No. 2 back contacts of relay 204, conductor 2I3, upper No. 3 contact-set of relay 20 305, lower winding of relay I04 to ground. Relay I32, however,does not operate in this circuit so that ground remains connected to the common start conductor H4. Relay I04, however, does operate, arrests the further movement of switch 23 I20 by opening the circuit of magnet I I3, extends the ground on its lower contacts to the terminal of the line engaged to brush I I9 and further locks in a circuit extending from ground on bank I.I1,

brush IIG, conductor I 38, lower No. 3 contact-set 30' of relay 30I, conductor I43, locking contacts of relay I00, upper winding of saidrelay, upper inner back contact of relay 204, conductor 2I4, lower No. 2 contact-set of relay 305, winding of relay II5, resistance I2I to battery, and at the 35 bottom back contacts of relay H0, in parallel with resistance I40 to battery. Relay II5 o'perates in this locking circuit and switches the link line conductors I22 and I23 through to the link circuit. Relay I03 now operates over the ex 40,.

tended line in a circuit which is traced from bat tery through its lower winding, lower normal contacts of relay I02, normal contacts of the No. 3 contact-set of relay IOI, lower N0. 3 contact-set of relay II5, conductor I23, brush I24 and line 45.:

terminal, subscribers loop, brush I25 and line terminal, conductor I22, upper No. 3 contact-set of relay H5, upper back contacts of relay IOI, upper normal contacts of relay I02, upper winding of relay I03 to ground. Relay I03 operates 50;

and closes ground through its upper contacts to the winding of relay IIO which operates and opens the circuit of relay 305 which now releases. Relay II5, however, does not release as a result of the release of relay 305 but is held looked over the lower front contacts of relay IIB to ground through its own lower No. 1 contactset. 'With the release ofrelay 305, relay I04 releases but the busy condition to brush H0 is now maintained by ground through the No. 1 contact-set of relay 60;,

H0 directly to brush H9. A circuit is now also closed for relay I05 extending from battery through the lower winding of said relay, conductor I41, normal terminal and brush 404, lower No. 3 back contacts of relay 304, conductor 348, 65;

DT connected to the normal terminal of brush Relay 7-0" 3|8 of connector 319, conductor 3&5, lower No. 5 back contacts of relay 22ft, conductor M3, lower No. 4 contacts of relay Hi1, lower inner back contacts of relay 20!, condenser 2E2, conductor lid, condenser I21, through the line loop as already traced, to ground through the upper winding of relay I03. The subscriber now dials the required number. If a local connection is desired, the digit 2 is dialed whereupon relay i653 will respond to two interruptions of the dial. When relay I03 releases on the first impulse, a circuit is completed from ground on the upper No. 3

' of relay IE6 to ground on conductor 3531.

contact-set of relay 392, conductor 3%, lower No. 4 back contacts of relay tilt, lower outer contacts of relay 20L conductor 245, No. 3 contacts of relay HB, lower inner contacts of relay W3, conductor Ml, winding of relay 3&1, upper No. 2 back contacts of relay 335, upper front contacts of relay H35, conductor 21?, winding of register magnet 49! of register M to battery. The magnet operates and, when the line is again closed after the dial interruption, brushes sea to 58 inclusive, or" register All advance to the first terminal. Relay 341 also operates in the dialing circuit but, being slow to release, remains in its operated position during dial interruptions and closes a locking circuit for relay I95 over its lower contacts, lower outer contacts of relay 3 31, to ground on conductor 381 so that when the brushes of switch H0 are stepped off the first terminal relay 105 will not release.

At the end of the second dial interruption, magnet 4!!! advances the brushes to their respective second terminals and relay 3t? releases whereupon relay H35 also releases. A circuit is now closed for relay it? extending from battery through its lower winding, conductor M2, N0. 2 terminal and brush 56 i, lower No. 3 back contacts of relay 3%, conductor 348, lower No. 2 contacts of relay 2B1, upper inner back contacts of relay 341, conductor 3 3$ upper No. 3 back contacts of relay I08, conductor 3S1, upper outer normal contacts of relay 26!, to ground on the front contacts of the upper No. 1 contacts of relay !!5. Relay E01 operates over its lower winding and locks through its upper winding, lower No. 3 front contacts, lower inner contacts or" relay 341, conductor 301, and thence as traced to operating ground on the contacts of relay H5.

Re1ay B is likewise provided with the same holding ground to its upper winding so that, when its locking circuit through the lower contacts of relay 351 is opened by the release of relay 3 5i,

relay H35 does not release.

With relay l0? operated, a self-interrupting circuit is established for register magnet 2-51! extending from battery through said magnet and interrupter contacts, brush 538 and the common terminals l to ii inclusive, conductor H2, upper outer front contacts of relay I 21 to ground. Register switch M6 is thus driven to the eleventh set of terminals where it awaits the dialing of the next digit of the called line. On the first impulse, relay 341 operates as before and completes a circuit for relay ifili extending from battery through the winding of said relay, lower No. 4 back contacts of relay 39 i, lower No. 1 contacts of relay E31, upper inner front contacts of relay 341, conductor 349, upper No. 3 back contacts Relay I03 operates and looks over a circuit path through its upper No. 1 contacts, lower No. 2 back contacts of relay 2%, lower No. l front contacts of relay H5, upper back contacts of relay tilt, con- 3 ductor M3, lower No. 3 contacts of relay 36!, conductor I38, brush H8 to ground. The operation of relay I06 now closes a circuit for magnet 306 of connector 3W extending from battery through the winding of said magnet, interrupter contacts, lower N o. 1 back contacts of relay 3%, upper No. 2 contacts of relay lilfi, lower back contacts of relay lilii, lower No. 4 front contacts of relay H5, upper back. contacts of relay I94, and thence as traced to ground on commoned contact bank 1 I1. Magnet 366, under the control of the back contact of relay Hi9, now drives brushes 3 to 320, inclusive, to the beginning of the required group of subscribers as more particularly described hereinafter.

Switch 3H], the trunk and line connector, has two groups of switching wipers, namely, wipers Ell-3M and 3l5-3l8 associated with a wiper switching relay 363. In the lower group of bank levels, subscribers lines certain P. B. X. groups only are connected, while in the early part of the upper group, outgoing trunk and tie line groups are connected. A single marking bank, that associated' with brush 3|9, is provided to which trunk group marking conductors and local subscriber group marking conductors are connected which extend to the bank associated with brush 4% of the register switch 4H). Hence, when the second digit has been dialed and brush 405' of register lill has been advanced to some terminal in the group of subscribers in which the called line is located, and the brushes of switch 3 I 0 have been advanced along the terminals of their corresponding banks until brush 3l9 connects with the local group terminal connected to the terminal on which brush 485 has been advanced, a circuit is completed for relay )9 which extends from battery through the winding of said relay, upper No. 2 contacts of relay 2S5, lower No. 3 back contacts of relay 204, brush 3i9 and group terminal included in the bracket line 349, terminal in the group to which brush 465 is connected, brush 465, conductor 358, upper No. 2 back contacts of relay 30I to ground. on the upper No. 2 front contacts of relay H5. Relay I99 operates, opens the driving circuit of magnet 3% and arrests any further movement of switch 310. At the end of the digit, relay 341 releases and relay 385 is reoperated in a circuit extending from battery through its upper winding, lower No. 3 contacts of relay I06, upper inner back contacts of relay 361, conductor 3 39, upper No. 3 front contacts of relay #93, upper contacts of relay it??? to ground on conductor 301.

It will be observed that the winding of relay 393 is connected through its continuity contacts to the odd terminals, beginning with the thirteenth of the bank of terminals accessible to brush 304. Remembering that at the time the subscriber began dialing the second digit the brushes of switch M0 were resting on their respective eleventh terminals, it is plain that if the second digit is an even one, brush 404 will be resting on an odd terminal of the bank at the time the switch comes to rest so that at the time the circuit for relay 3% is closed, a parallel cir cult to relay 303 is simultaneously completed through the lower No. 2 contacts of relay I66, conductor MB, lower No. 3 back contacts of relay 3534, brush 40 i and cooperating odd terminal, lower No. 1 normal contacts of relay 303, winding of said relay to battery. Relay 393 operate: and switches over the wipers of connector 310 to the required outlets on the lower set of banks. On the other hand, if the digit dialed is odd, brush W4 will be resting on an even terminal and the parallel branch of the circuit to the winding of relay 303 will not be closed, in which event the wipers connected to the normal contacts of relay 303 will be operative to extend the connection to a line on the upper set of banks.

The operation of relay 305 indicates that the second digit has been received. The third digit is now dialed, but instead of register magnet I responding to the dial impulses, trunk connector magnet 306 is operated on the impulses over a circuit extending from battery through the winding of magnet 306, upper No. 2 contacts of relay 305, winding of relay 347, conductor I4I, back contacts of relay I 03, upper No. 3 contacts of relay H0, conductor 2I6, lower outer back contacts of relay 20!, lower No. 4 back contacts of 34'! and, when relay 34'! releases at the end of the digit, a circuit is completed for relay 204 extending from battery, resistance 208, winding of relay 204, lower No. Z'contacts of relay 300, lower No. 3 contacts of relay 305, lower No. 1 contacts of relay I00, lower No. 3 back contacts of relay I01, lower inner contacts of relay 341, conductor 30? to ground. The operation of relay 204 com-- pletes a circuit for relay 2! 8 extending from battery, resistance 2I I, the top No. 2 front contacts of relay 204, winding of relay 2I8, lower No. 3 contacts of relay 305, lower No. 1 contacts of relay I06, lower No. 4 back contacts of relay I01, lower inner contacts of relay 341, conductor 30! to ground. Both relays 204 and M8 look over their lower No. 1 contacts to ground on conductor'301.

Now if the called line is an individual line, relay I09 will be held operated in a circuit over the upper No. 2 contacts of relay 200, lower No. 3 front contacts of relay 204, top inner back contacts of relay 303, brush 3 I4, and terminal multipled to conductor 350, conductor 35!, upper No. 2 back contacts of relay 30I, upper No. 2 front contacts of relay H to ground. This ground is multipled on the bank accessible to brush 3I4 only for regular lines, last lines of private branch exchange groups and trunk groups. Due to the fact that there is a single marking bank (that accessible to brush 3 I4) for group discrimination and hunting and that trunk groups and subscribers lines occupy corresponding positions in the two banks of switch 3I0, it is necessary to segregate the private branch exchange groups in that portion of the bank not occupied by trunk groups. It will also be observed that relay I09 will always operate independently of the circuit above traced through brush 3M if relay 303 has operated; the circuit, in this case, being completed to ground on the top inner front contacts of relay 303. The reason for this is that all private branch exchange groups having numbers in the odd tens group are segregated on the lower set of banks.

With relay 204 operated, relay I04 is now used to test if the wanted line is free. If the line is free, then a circuit is completed from ground through the lower winding of relay I04, upper No. 3 contacts of relay 305, conductor 2 I3, lower No. 2 front contacts of relay 204, lower No. 2 front contacts of relay 303, brush 3I6, respectively, of

I releases.

switch 3I0 to battery through the cut-off relay in the called line circuit (not shown). Relay I04 now looks over ground through brush II6, con-- ductor I38, lower No. 3 contacts of relay 30l, conductor I43, upper front contacts and upper 5 winding of relay I04, top- No. 1 front contacts 01' relay 204, winding of relay 30I to battery, operating the latter relay which then looks over its lower No. 4 contacts to ground onconductor 301. Relay I04 further connects ground to brush 3I6 10 for operating the cut-off relay of the called line, this ground extending from the lower contacts of relay I04, conductor 2I3, lower No. 2 front contacts of relay 204, lower No. 2 front contacts of relay 303 to brush 3I0.

When relay I04 operates, the locking circuit of relay I06 is broken at its upper back contacts 7 causing this relay to release which, in turn, opens the circuit of relay 305 which releases also. Further, since the ground multipled to the terminals of the bank accessible to brush 3 is extended over the upper No. 2 back contacts of relay 30I, then, when relay 30I operates this ground is disconnected from brush 3| 4 whereupon relay I09 When relay 30I operates, ground is connected to the battery side of the locking circuit of relay I04 through the lower No. 2 contacts of relay I causing said relay to release. But the line cut-off relay. is now held directly from this ground since it extends to the lower No. 2 80 contacts of relay 303. The line is, therefore, held and the tip and ring conductors from the link are switched through to the called line over the upper and lower No. 1 contacts of relay 30I.

The called subscribers line will now be rung from the link over a ringing circuit extending from source of current R, upper winding of relay 300, lower No. 3 back contacts of relay 300, lower No. 1 contacts of relay 30 I, lower No. 1 back contacts of relay 302, lower No. 3 front contacts of 4,0 relay 303, brush 3|! and terminal, subscribers loop (not shown), brush 3 I5, top No. 2 front contacts of relay 303, top No. 1 front contacts of relay 30I, top outer back contacts of relay 300, resistance 35I to battery and ground. When the subscriber answers, relay 300 will operate and break its lower No. 1 contacts whereupon relay 300 will then remain operated in parallel with relay 30I over its lower winding. The operation of relay 300 removes ringing from the line and switches the tip conductor 300 from resistance 35I to the winding of relay II2, the other side of which is connected to ground upper No. 2 back contacts of relay 304. It further switches the ring conductor 309 over its No. 3 bottom front contacts, conductor I48, upper No. 2 back contacts of relay 220, bottom outer front contacts of relay I 03,'winding of relay III, conductor 4I4, lower No. 1 back contacts of relay 304, resistance 322, to battery. Both of these relays operate 00 over the called subscribers loop, the operation of relay II2 closing a circuit to relay I02 from ground through its left contacts, causing said relay to operate .and reverse the calling loop at its top and bottom outer front contacts. On this type of call, however, this reversal has no effect since relay I03 remains operated on the reversed as well as the direct current flow.

If the calling line is equipped for metering, then when relay II2 operates, a ground impulse is transmitted from the metering impulse circuit MPC along conductor 2I9, right contacts of relay 2I2, lower No. 3 contacts of relay 2H3 to resistance 208 and effects a short circuit of the winding of relay 204 and causes said relay to re- 15.

lease. If the link is equipped to provide for multi-metering, then when relay 204 is released, metering impulses will be transmitted to the subscribers meter as more particularly described hereinafter. If, however, the link is to be arranged for single metering only, solid ground is connected to the right contacts of relay H2 and causes the short circuit and release of relay 204 as already described. Under such circumstances, the metering impulse circuit MPC is not provided and permanent ground is connected to conductor 4I9 whereupon, after the. release of relay 204, relay 2I3 is short-circuited through lower No. 4 contacts of relay 2 I8, top No. 2 back contacts of relay 204, resistance 2II to battery, causing said relay to release. Relay 2I8 is, however, of the slow release type and, during the time it is still operated, a circuit is completed extending from ground through the winding of the calling subsoribers meter I44, brush I27, upper No. 3 contacts of relay 2H3, lower No. 2 contacts of relay H5, lower No. 4 back contacts of relay 204, lower No. 2 back contacts of relay 304, lower No. 3 back contacts of relay 220, resistance 405, to battery. In link circuits equipped for single metering, as for the case now temporarily assumed, resistance 405 is multipled to terminals I2 to 2|, inclusive, on the bank accessible to brush 408 of register switch 4I0 corresponding to lines that are to be metered. In a link circuit equipped for multi-metering, the meter pulse will be received from the meter circuit MPG to be described later.

At the termination of the conversation the calling subscriber restores and opens the circuit of relay I03 which releases and opens the circuit of relay IIO. Relay IIO releases cut-off relay I32, unlocks relay I15 which in releasing disconnects ground from, the holding conductor 30'! whereupon all relays locked thereto are restored to normal. A self-driving circuit is now co pleted for finder magnet I I3 extending from battery through its winding and interrupter contacts, lower No. 4 back contacts of relay H5, top back contacts of relay I04, conductor I43, lower No. 8 contacts of relay 30I, conductor I38, brush IIB, bank III to ground. The finder switch brushes are thereby restored to their normal terminal where the driving circuit is broken.

When relay H5 releases, a driving circuit for register magnet 40I is also completed, extending from battery through its winding and interrupter contacts, brush 406 and connecting terminals, conductor M I, top inner and outer back contacts of relay I01, to ground on the upper No. 2 back contacts of relay II5. Inasmuch as all the terminals beyond the eleventh and accessible to brush 406 are commoned to conductor M I the switch magnet will drive the switch brushes until their respective normal terminals are reached.

Call to a private branch exchange subscriber If the call is to a private branch exchange subscriber, connector 3I0 is positioned on the required line in the manner already described. None of the outlets of private branch exchange groups on the bank accessible to brush 3I2 is connected to ground except the last line of each of the groups so that when relay 204 operates (on the first pulse of the third digit), relay 1569 releases since no ground is available on brush 3I2 at the time the brush advances to the first line of a private branch exchange group. Relay I04 new tests the called line as before. Should the line be busy and relay I04, therefore, should fail to operate then, inasmuch as relay 305 is reoperated after the second digit and relay 2|.8 on the first pulse of the third digit, a self-interrupting circuit for magnet 306 is provided extending from battery through the winding of mag- 15 net 306, interrupter contacts of said magnet, lower No. 2 contacts of relay 2I8, lower No. 1 contacts of relay 305, upper No. 2 contacts of relay I06, lower back contacts of relay I09, lower No.4 front contacts of relay II5, backcontacts of relay I04, conductor I43, lower No. 3 contacts of relay 30I, conductor I38, brush H6 to ground. The switch magnet, therefore, will continue to advance its brushes under the control of relays I09 and I04. When it reaches the terminals of a free line, relay I04 will operate as already described. If no free line in the group is available, the switch brushes are advanced to the last outlet of the group which is connected to ground over the terminal accessible to brush 3I2 and relay I09 is operated over its holding circuit in the case of an individual line, as already described. If the last line is free, the test circuit for relay I04 is completed causing said relay to operate as described and hold the line for future operations. If the last line is busy, relay I09 operates, relay I04 remains normal and a. circuit is completed for relay 200 extending from battery through the winding of said relay, lower No. 3 normal contacts of relay 302, upper No. 2 contacts of relay 2I8, lower front contacts of relay I09, lower No.4 front contacts of relay I I5, back contacts of relay I04, conductor I43, lower No. 3 back contacts of relay 30I, conductor I38, brush IIS to ground. Relay 200 is made slow to operate so that if relay I04 should come up in the meanwhile, relay 200 will not operate. Busy tone is now connected to the calling line from source of tone BT, upper No. 2 contacts of relay 302, lower No. 3 contacts of relay 200, lower inner back contacts of relay 20 I, condenser 2I2, conductor 4I4, condenser I21, over the calling loop as previously traced to ground through the upper winding of relay I03.

Disconnection now takes place as previously described when the calling line restores. 5 In the above description of a call to a P. B. X. subscriber, it has been assumed that the lines of the P. B. X. group are located in the top half of the terminal banks of connector 3I0 and that the sleeve conductor of each of the lines is accessible to brush 3 I2. However, the P. B. X. group may be located in the bottom half of the terminal banks of connector 3 I 0, in which event the second digit of the P. B. X. group would be such as'to cause brush 404 of register 4I0 tobe positioned on an odd terminal whereuponrelay 303 will be operated and the P. B. X. group would be reached by brushes 3I5, 3I6 and SH; brush 3|! contacting with the sleeve conductor of the lines in the group. 0

Calls to main-automatio exchange The trunks to the manual exchange are used for extending calls to a manual board and to any automatic train which may be reached by way of the manual exchange. If a call to an operator is desired, the digit 0 is dialed; if the automatic equipment is required the digit 9 is dialed. In either case the link is seized by the calling line in the manner described for a local call. The register switch 4I0 responds to the first digit and its brushes are driven to the set of. terminals corresponding to said digit, indicating thereby the trunk group required. If the digit 0 is dialed for a call to the operator then, when relay 34! releases at the end of the digit, relay 220 operates over a circuit extending from battery through the winding of said relay, conductor 22 I, strapped to terminal in the bank accessible to brush 404, brush 404, lower No. 3 back contacts of relay 304, conductor 348, lower No. 2 contacts of relay I01, (relay I01 not having operated since brush 404 did not stop on the second terminal) top inner back contacts of relay 341, conductor 349, top No. 3 back contacts of relay I06, to ground on conductor 301. Relay 220,.on operating, locks to ground on conductor 301 through its lower No. 2 front contacts.

A circuit is now closed for relay I 06 extending from battery through its windings, lower No. 4

contacts of relay 220, lower No. 2 back contact of relay 200, lower No.4 front contacts of relay Il5,'topback contact of relay I04, conductor I43,

lower No. 3 back contacts of relay 30!, conductor I38, brush IIB, to ground. The operation of relay I06 now causes a driving circuit to be closed for the trunk connector magnet 306 extending from battery through its winding, interrupter contacts,

' as cross-connected to the particular junction ter- ''minal in the terminal bank accessible to brush 405. When the first terminal of the trunk group is reached by brush 3I9 and relay I09 operated as previously described, a circuit is completed for relay 305 extending from battery through its upper winding, lower No. 3 contact of relay I06, top inner back contact of relay 341, conductor 349, upper No. 3 front contact of relay I06, top contact of relay I09 to ground on conductor 301. The previously described circuits for relays 204 and 2l8 are now completed causing these relays to operate, while a testing circuit is provided for relay I04 extending in part from ground through the lower winding of said relay, upper No. 3 con tact of relay 305, conductor 2 I3, lower No. 2 front contact of relay 204, lower No. 2 back contact of relay 303 to brush 3I2 and terminal.

When the brushes of switch 3I0 reach a free trunk, relay I04 operates in a circuit completed over brush 3I2, sleeve conductor 508, right contacts of relay 502, right outer back contacts of relay 501, left outer contacts of relay 506, left middle contacts of relay 504', right outer contacts of relay 50I, both windings of relay 505 (the right winding extending through the right inner back contacts of relay 505) to battery. It will be observed, however, that the driving circuit of magnet 306 is controlled through the bottom back contact of relay I09 while the holding circuit of relay I09 (after the operation of relay 204) in turn depends on the presence of ground on the terminals of the bank accessible through brush 3 I 4. However, the trunk groups, on this bank are so wired that no ground is connected to the terminals of the trunk groups except for the last trunk'in each of the groups which are then multipled together through a conductor connected fore will continue to drive over the trunk group as described for private branch exchange groups and, if a free trunk is found, relay I04 will oper-- ate and open the circuit of magnet 306. If all the trunks in the group are busy, magnet 306 will 5 continue to operate and drive the brushes to the last trunk of the group where relays I09 and 200 operate as before and furnish the subscriber with the busy signal.

If a trunk is found, relay 505 operates in the 10 above described circuit, disconnects relay 502 at its left outer and middle back contacts from conductors 509 and M0 extending to the banks of line finder I20 for inward calls and operates relay 506 in a circuit which extends from battery through its winding, right outer contacts of relay 504, right inner back contacts of relay 501 to ground on the right middle front contacts of relay 505. Relay 506 operates and removes the high resistance relay 503 from the line. In this type of a call, however, and since the top No. 1 contacts of relay 220 are open, the ground 7 connection from conductor 301 through lower No. 4 contacts of relay 30I to the battery side of the lower Winding of relay 300 is missing at the time said ground is applied to the Winding of relay I. Relay 300, therefore, will operate in parallel with 30I and no ringing is applied over the called trunk. With relay 220 operated, a trunk is seized with relay III connected to the ring and relay 30 I12 to the tip thereof through a signalingloop (not shown) in the trunk at the main exchange and this condition causes the distant end of the trunk to switch direct to an operator in any suitable manner. 4 3? When the call is released, the link circuit removes ground from conductor 508 and relay 505 releases, whereupon relay 504 releases. During, the slow release of relay 506, the high resistance relay 503 is applied to the tip and ring conduc- 4Q tors 509 and 5I0, respectively. If there is battery in'either conductor due to a busy flash, relay 503 will operate and hold relay 506 over ground on its left contacts, thereby maintaining the busy condition for the trunk. jWhen relay 503 releases, relay 506 will release, causing the trunk to test free. Thus the trunk is held busy at the incoming end until it is free at the distant end.

If the call originates froma coin box subscriber a circuit is closed for relay 202 extending from 5 battery through resistance 203, conductor 2I5, terminal and brush I26, conductor I44, winding of relay 202, to ground on conductor 301. (Relay 202 would also come up on a local call from a coin box subscriber, but without efiect as de scribed hereinafter.) With relays 220 and 202' operated, with the consequent opening of the upper No. 2 back contacts of the former and the lower No. 4 back contacts of the latter, the battery extended through to the ring side of the line is now through resistance 322, and since resistance 322 is high, it imposes a marginal condition at the terminating end of the trunk which is used to cause the distant end of the trunk to give a discriminating coin box signal (not shown) either by flash or by lighting a coin box calling lamp in any suitable manner.

When the operator replies, battery is connected to the tip side of the trunk and ground on the ring (not shown), that is, to conductors 5I0 and 509, respectively, whereupon a circuit is completed for relay I I2 to ground on the upper No; 2 back contacts of relay 304, and relay III is operated to' battery through resistance 322. on the lower No. 1 back contacts of relay 304 if, at this time relay 202 is released as described below since, with resistance I55 in the ring side of the line, relay III cannot operate. The operation of the link circuit after relay II 2 operates is, in this case, the same as described on a local call except that contact I0 on the terminal of the register switch 4 I0 accessible to brush 408 is not connected to resistance 405, as in the single metering case, or to a meter pulse lead as in the multinietering so that no battery potential is extended to the subscribers meter during the releasing time of relay I00 as previously described. In general, metering is not required on 0 level calls.

With relay II2 operated, an obvious circuit is closed for relay I02 which, when operated, holds relay IIO operated over a circuit path from battery through the winding of relay H0, upper No. 4 front contact of relay 220, upper inner front contact of relay I02, to ground on conductor 301. Relay I02 also connects ground to resistance 203 via its lower inner contacts to shunt relay 202 which, upon releasing, again shunts resistance I65 from the ring side of the line and thereby causes the operation of relay III as already described.

Should the calling subscriber hang up in this case, relay I 03 will release, followed by the release of relay III. But his line circuit is not cleared until the operator releases the call. She can, if she desires, re-ring the calling line by applying ringing current from the ringing key of her cord (not shown) to the ring side of the line to operate relay IOI over the following path: ground through the winding of relay IIlI, condenser I3I, contacts of relay III, upper No. 2 front contact of relay 220, bottom No. 3 front contact of relay 300, conductor 309, No. 1 back contacts of relay 302, No. 3 armature of relay 303, brush 3! I and terminal, ring side of the outgoing trunk to ringing source in the operators cord (not shown). With relay IIII operated, ringing current is now locally applied to the calling line in a circuit extending from ringing source RI, upper No. 3 contact of relay 220, lower No. 3 front contact of relay IOI, bottom No. 3 front contact of relay II 5, conductor I23, brush I24, over the subscribers loop, brush I25, conductor I22, upper No. 3 contact of relay II5, top front contact of relay IOI, upper No. 5 contact of relay 220 to battery and ground through resistance I. When the subscriber answers, relay I03 operates followed by relay III and relay IOI will release.

On an incoming call, a loop is applied to the distant end of the trunk end, as a result relay 502 operates in a circuit extending from battery through its winding, right inner back contact of relay 506, right outer back contacts of relay 505, operators loop, left middle back contacts of relay 505 to ground on the right outer back contact of relay 505. Relay 502 operates and closes a circuit for relay 50'! extending from ground on the right middle back contact of relay 505, left front contacts of relay 502, winding of relay 531 to battery. As a result, a start signal is extended to the link from ground on the left outer contacts of relay 504, rightinner contacts of relay 50I, right outer back contacts of relay 505, left inner contacts of relay 50?, conductor 5II connected to the start conductor I I4. A free link hunts for the trunk and serves it since the link test relay I04 tests over conductor 5I2 and operates to battery over a circuit which extends through the right outer front contacts of relay 501, left outer contacts of relay 500, left middle contacts of relay 504, right outer contacts of relay 50I, right inner back contacts of relay 505, right and left windings of relay 505 to battery. Relay 505, however, only operates when solid ground is connected to conductor 5I2 in the same way as described for a local call. As a result, relay 502 releases followed by the slow release of relay 501. During the interval in which relay 507i is releasing, a circuit is closed for relay 50 extending from battery. through the right inner front contacts of relay 501 to ground on the right middle front contacts of relay 505. Relay 50d operates and looks over its right inner contacts to operating ground. Dialing is direct on to relay I03 in the link, the setting up of which, on the terminals of the wanted line, is the same as already described.

When the called subscriber answers, relay I02 in the link operates, reverses the tip and ring of the line and serves to extend metering and supe vision to the main exchange in any suitable manner such as by polarized apparatus responsive to the reversal of current.

On the release of the call, relay 505 deenergizes when ground is removed from conductor 5I2. If there is still a loop on the calling side of the line due to a trouble condition, relay 502 reoperates when relay 505 releases and reoperates relay 501 over the left front contact of relay 502 to ground on the right middle back contacts of relay 505; relay 50% holding in the meanwhile over its left inner contact to ground on the left outer contacts of relay 501. When the holding loop is broken, relays 502, 50'! and 50% release and the trunk is free. The slow release times of relays 50'! and 500 give an adequate guard to govern the release of any slow release relays at the distant calling end.

If, for any reason, impulsing stops before the trunk on an incoming call has been served by a free link, relay 502 responds to the impulses and holds relay 507 during the impulse transmission. A circuit is then completed for relay 50I extending from battery through its windings, left middle contacts of relay 501, left back contacts of relay 502 to ground on right middle back contacts of relay 505. Relay 50I operates and then looks over its own left inner contacts.

The operation of relay I disconnects the start conductor 5I2 at its right outer contacts, busies the trunk by removing the windings of relay 505 from conductor 500 at its right outer contacts and 5 on the right outer back contacts of relay 506. l

The circuit is then held in this condition until the distant end releases.

If, on outgoing calls from the local exchange, split ground signaling is used and delayed metering is necessary or, on incoming calls to the local exchange, loop dialing is required, the trunk circuit shown to the right of Fig. 5 is used instead of that to the left of the figure, which trunk further provides ring back tone on outgoing calls if no tone is supplied in the manual exchange.

On outgoing calls with this trunk, the digit 0 is dialed and, of course, relay 220 operates as already described. The switch 310 is then driven therewith resistance 524 tov battery. Relay 516 operates and looks over its right outer front conta'ctsto test conductor 519. The trunk is now busy to other link finders by ground on conductor 520, through the right inner contacts of relay 516, and the start conductor 511 is broken at right middle contacts of relay 516. Ring back tone is now returned to the calling subscriber over a path extending from source of tone RL, condenser 521, left outer contacts of relay 516, right middle back contacts of relay 515, conductor 521 terminal and brush 3! I over the calling subscribers loop through the link back to brush 313 and terminal, conductor 522, through the opera tors loop, right inner back contactsof relay 515, winding of relay 514 to battery. The left middle back contacts of relay 516 remove ground from conductor 522, and the operator receives a calling signal due to the presence of battery through resistance 322, relay 111, on the ring side of the line from the link. If the calling line is a regular subscriber, that is, a non-coin box line, then relay 202 is normal and the battery signal on the ring side of the line islow, due to the fact that resistance 125 is short-circuited as already described and the marginal coin box signal in the operators loop is operated to indicate a non-coin box line. If, on the other hand, a coin box line is calling, relay 202 is operated, the battery signal is of high resistanceand the marginal coin box signal is not operated. In the case of the low resistance condition, relay 111 operates in the link but not on the high resistance condition.

When the operator answers, one leg of the trunk is grounded and relay 515 operates, in turn operating relay 5!? over an obvious circuitwhile, at the same time,'a circuit is completed for relay 515 from battery through its winding, right inner contacts of relay 518, left contacts of relay 511 to ground on the right inner contacts of relay 7 516, said relay looking over left outer front contacts to operating ground. Relay 518 now operates over an obvious circuit to ground on the left inner contacts of relay 515 and looks over its 'left contacts to ground on the right outer contacts of relay 51']. Ring tone BL is now disconnected from the line at the right middle back contacts of relay 515 while the right middle front contact of this relay switches the operators circuit on to the line conductors 521 and 522. Re lay 514 is disconnected at the right inner contacts of relay 515 and releases, but relay 511 is held over the right middle contacts of relay 515.

The ground on the right inner contacts of relay 511 is connected to conductor 523 which, in turn, is connected to a terminal in the bank accessible to brush 313 of switch 310. If relay 220 is op- .erated, indicating an operators call, then the fact that the lower No. 5 front contacts of relay 220 are operated causes the ground on conductor 523 to be connected to conductor 345 to shortcircuit relay 252 which, if operated, (as it would be on a coin box call) releases and short-circuits resistance 145 in series with relay 1 1 1 so as to operate the'rnarginal coin box signal in the operators circuit and indicate thereby that the coin has to be collected by the operator. Conversation may now proceed between the operator and the calling subscriber.

If the operator completes the call and desires to operate the calling subscribers meter, she presses her meter key in the cord circuit (not shown) which replaces the ground on both conductors of the trunk with a metallic loop. As a result, relays 111 and 112 in the link operate in series through the loop and the call will be me tered due to the operation of relay 102 following the operation of relay 112 as already described. It will be noted that no battery is required at the manual exchange in order to complete this call 5 so that this type of work is suitable for use to magneto offices.

When making a call to. the exchange, the operator at the manual exchange loops the trunk, as a result of which relay 514 operates. Relay 10 511 then operates and'extends a start signal to the link over the right outer contacts of relay 511, left back contacts of relay 518, right middle back contacts of relay 516 to start conductor 511. The left contacts on relay 511 further serve to close battery through the winding of relay 515 to conductor 520 which serves to operate relay 104 at the time the link has searched for and found the calling trunk. Relay 515 also operates in the test circuit, locks up to ground supplied to conductor 520 through the lower contacts of relay 104, disconnects relay 514 and ground from the calling loop and further switches the calling loop through to relay 103 in the link over its right middle front contacts. The operation of relay 515 further closes an obvious circuit for relay 518 which also operates and locks to ground on the right outer contacts of relay 511.

The operator now dials directly into the link and gets reverse battery supervision back from so the link when the called subscriber answers.

If two-way trunks with battery dialing are required between the local exchange and the manual exchange, then a trunk circuit of the type shown on the left of Fig. 6 is used. On outgoing ates as already described for the trunk immediately preceding, that is, by connecting ground on brush 312. As a result, relay 601 operates in a circuit which extends from ground on said brush, conductor 605, right outer contacts of relay E00, winding of relay 601 to battery and, in parallel with resistance 606 to battery through its left inner contacts and left inner contacts of relay 605. Relay 601 operates and switches the line through its right inner and outer front contacts by short-circuiting condensers 606 and 601. The tip and ring conductors are, therefore, connected straight through to the manual end. A calling signal and coin box discrimination signal are given by battery through relay 1 1 1' as already described and, when the operator answers, battery is put out on the line to operate relay 1 12 and gives the operator hold and metering if the link is arranged to do so. When making an incoming call to the local exchange, the operator extends ground on the ringside of the line and operates relay 603. Relay 602 now operates over an obvious circuit and connects ground over its right outer contacts, left outer contacts of relay 601, left outer back contacts of relay 600, to starting conductor 511 whereupon a link is started to find the calling trunk. When brushes 125 and 124 connect with the trunk terminals, a loop is closed extending from battery through the lower winding of relay 1 )3 to brush 124 and terminal as previously described, conductor 620, left contacts of relay 602,

, right contacts of relay 603, right inner back coninner contacts to the ground on the No. 2 contacts of relay I04, also as previously described, While the operation of the breaking of the right outer contacts of this relay serves to busy the link to outgoing calls. When the operator throws the dial key (not shown), battery is extended on the tipside of the trunk causing relay 504 to operate and open the loop holding relay I03 which now responds to further dial interruptions. The call is thus set up in the link end, when the wanted subscriber answers, the link tip and ring conductors are reversed by relay 92, as already described, while brush I26 and its cooperating contact is grounded by the bottom inner front contact of relay I02. Inasmuch, however, as conductor 003 is connected to the trunk outlet on the terminal cooperating with brush I26, relay BBI operates to said ground. The right inner contacts of said relay break the pulsing loop while its right front contacts switch the trunk through to the link. Relay I03 now holds to the distant manual end. Since the talking leads are reversed by relay I02, relay I03 will hold over its grounded winding to the battery which operated relay 603.

When the called subscriber restores, relays H2 and I I I release, in turn followed by the release of relay I 03. Since, however, relay Gill also releases at the time the bottom inner contacts of relay I02 are open, relay 603 is again put out on the line. Relay 6513 now operates and, in turn, operates relay 602 whereupon the link relay E03 will be reoperated over the local loop made by the contacts on relays 602 and 603. The operator now receives correct supervision since there is now ground on both conductors of the local trunk.

Call to the automatic equipment of the main exchange A subscriber wanting to make a call to a subscriber reached by the automatic equipment in the main exchange dials 9 for the first digit. Switch M0 responds to this digit in the usual manner. In this case, however, instead of relay 220 operating, as in the case of an operators call, relay 3 24 operates in a circuit which extends from battery through the winding of said relay, terminal block H5 and conductor extending to terminal No. 9 of the bank of terminals accessible to brush 404, brush .04, lower No. 3 back contact of relay 3:34, conductor 348, bottom No. 2 contact of relay I01, top inner back contact of relay 341, conductor 349, upper No. 3 back contact of relay I03, conductor to ground. Relay 304 operates and looks over its upper No. 4 front contact to ground on conductor 301.

The same group of trunks are now searched by switch 3I0 as in the case of a zero level call, due to the fact that outlets 9 and I0 on terminals accessible to brush 405 of the register switch 4I0 are common to the same group of trunks beginning with conductor on terminal I0 accessible to brush 3!!) of switch 3I0. With relay 304 operatcd, a circuit is now completed for relay I06 extending from battery through the winding of said relay, bottom No. 4 front contact of relay 304, bottom No. 2 back contact of relay 200, bottom No. 4 front contact of relay II5, back contact of relay I04, conductor I43, bottom No. 3 back contact of relay 30L conductor I38, brush H6 to ground. Relay I05, which was operated at the beginning of the digit, is released at the end as already described so that no further digits will effect switch 4H3.

Trunk switch magnet 300 is now reoperated over a self-interrupting circuit previously traced through the bottom No. 1 back contact of relay 305 and top No. 2 contact of relay I03 and bottom back contact of relay I09, and the brushes of said switch are driven to the beginning of the trunk group whereupon relay I03 operates as already described for a zero level call. Each of the trunks in the group is now tested as before and a free one is seized as in the zero level call. If all the trunks are busy, the brushes of switch 3! will run to the last trunk whereupon relay I09 will operate over a circuit extending from battery through the winding of said relay, upper No. 2 contacts of relay 209, lower No. 3 front contacts of relay 204, upper No. 1 back contact of relay 303, brush 3I4 and cooperating last terminal of the trunk group, conductor 352 to ground on the lower No. 1 contacts of relay 220.- In case of an all trunks busy condition, therefore, and in a connection involving the automatic equipment at the main exchange, the switch 3I0 will stop on the trunk preceding that to which the recall circuit mentioned in the zero level call is connected. This recall circuit can, therefore, only be seized by calls which are dialed zero. When a free trunk is found, relays I04 and 30I will operate as before and the tip and ring of the line are switched through to the outgoing trunk. Since relay 304 is operated and relay 220 released, relay 300 operates and holds in parallel with relay 30I and therefore no ringing is sent out to" the trunk. Further, since relay 304 is operated, a metallic loop is closed through to the outgoing trunk in the line extending from the tip conductor 308, top outer front contact of relay 300, winding of relay II2, top No. 2 front contact of relay 304, winding of relay I I I, bottom outer contact ofv relay I03, resistance I45, bottom No. 3 front contact of relay 300, to the ring conductor 309. This loop is closed through the regular line relay to battery and ground at the incoming selector of. the automatic train at the main ofiice (not shown).

Calling subscriber now dials the directory number of the wanted line. These further digits, instead of being received by register switch MD, are repeated over the trunk to the distant automatic train over a loop extending from ground on the tip side of the trunk (not shown), top outer armature of relay 303, top No. 1 contacts of relay 30I conductor 308, top outer front contact of relay 300, top No. 1 contact of relay 304, top outer front contact of relay 34?, bottom outer front contact of. relay I03, resistance I45, lower No. 3 front contact of relay 300, conductor 309, bottom No. 1 front contact of relay 30I, lower N0, 1 back contact of relay 302, to the ring side of the line and thence to battery and ground in the trunk. During the pulsing the outer front contacts of relay 341 are used to short out the high impedance bridge provided by relays H2 and III in series, since relay 347 comes up either in series with the winding of magnet I for further digits used for multi-metering discrimination as described hereinafter, or to battery on relay I05 through the upper No. 2 back contact of relay 305 for digits not required for discrimination, or for all digits in the single metering case. Since the equipment in the automatic exchange provides battery on the ring side of the line and ground on the tip side, relay I I will operate whenever relay 34? is back after the distant end has been seized. This operation, however, has no function in this type of call. Further, relay I I 2 will not operate at this instant since rectifier 323 is low resistant to current in not required in the present call.

If the link is to be used for single metering only on calls of this type, terminal No. 9 on the bank accessible to brush B is strapped to resistance 405 and the calling subscribers meter will receive a battery pulse through a circuit path which extends from resistance 405, brush 408, lower No. 2

front contact of relay 304, lower No. 4 back contact of relay 204, lower No. 2 contact set of relay II 5, upper No. 3 front contacts of relay 2 I8, brush I21 and terminal, winding of register magnet I44 to ground, during the releasing time of relay 2I8 after relay 204 has operated. 'If, however, it is not required to meter a call of this type, terminal 9 is left blank so that no metering pulse is sent out. If. the link is used for multimetering, then the metering will take place as described hereinafter.

If the call to the automatic equipment of the.

main exchange originates from a coin line, then relay 202 is operated at the time the link is seized,

asfalready described. No coin box signal, however, is sent out to the distant oflice since, in this case, the lower No. 4 contacts of relay 202 are short-circuited by the No. 2 back contacts of relay 220. If it is required that coin box subscribers shall not have access directly to the main automatic equipment, then terminal 9 on the bank of terminals accessible to brush 404 is connected to terminal I I which, in turn, extends to the armature of the lower No. 3 contact set of relay 202. Under such circumstances, when the calling subscriber dials 9 a circuit is completed for relay 20I extending from battery through its upper winding, lower No. 3 front contacts of relay 202, eleventh terminal cross connected to the ninth terminal on the bank accessible to brush 404, upper No, 4 contacts of relay 304, to ground on conductor 307. With the operation of relay 2|, the calling subscriber receives NU tone over a circuit extending from source of tone on the bottom inner contact of relay 20l, condenser 2I2, conductor 4, condenser I21 and thence as previously traced through the subscribers loop, back toground through the upper winding of relay I03.

-The operation of relay 20I further locks said relay to its lower winding through its upper outer contacts to ground on the upper No. 1 front contacts of. relay H5 while ground is disconnected from conductor 30'! thereby releasing all relays locked thereto.

Trunk to subsidiary exchanges the contacts corresponding to these digits on the terminals of the bank accessible to brush 404 are wired to the upper winding of relay 20L I If,

therefore, a dead code is dialed, relay 20I will operate and give NU tone to the subscriber as already described. Inasmuch as the register magnet impulse circuit from the inner contact of relay I03 is carried through the bottom outer back contact of relay 20I, further impulsing is prevented after the dialing of a dead digit while the holding conductor 30'! is broken at the top outer contact of relay 20I so as to drop oii all relays holding thereto. Terminal 5 on the bank of terminals accessible to brush 404 is shown connected to the Winding of relay 403 in connection with the use of switch M0 for digit absorption when the digit 5 is dialed. Digits 6 and 8 give access to subsidiary automatic exchanges and digit '7 gives access to a subsidiary manual exchange. Combined automatic and manual working is not given to these subsidiary exchanges.

If the digit 6 is dialed, relay 304 will operate at the end of the digit over a circuit completed to brush 404 on contact 6 thereof and the required group of trunks Will be marked by relay I09 over the marking conductors from the bank of terminals accessible to brush 3l9 to contact 6 of the terminal accessible to brush 405. The circuit will operate exactly as described for a main office automatic call except that the required group of trunks will be tested.

If the digit 8 is dialed, operation would be exactly similar for the third group of trunks to be tested. If digit '7 is dialed then relay 220 will operate at the end or" the digit in a circuit completed over the terminal I accessible to brush 404 and the operation will be exactly as described in the call to the main oilice zero level.

Incoming trunk caZZTrtmk ofiering When a call is made on an incoming trunk, the

trunk is found and seized by a link circuit as a I calling subscribers line is found in a local call. The operations are similar to those described for other classes of calls since it is possible for the trunk to be connected either to a-local subscriber, or through the link to a trunk to a dis tant exchange. In calls to a local subscriber, if the subscribers line is busy, relay 200 operates in the link and busy tone is transmitted back over the calling loop in the usual way.

If the call is from an operator, she canoffer the call to the busy line by operating her ringing key. This puts ringing current to the ring of the line and operates relay IEI over a circuit extending from the ring side of the incoming trunk (not shown) brush I24, conductor I23,,

lower No. 3 contact of relay I 55, lower No. 1 contact of relay 200, condenser 13!, winding of relay IN to ground. The operation of relay IOI causes the release of relay 03, but relay H0, which is held operated from the top contact of relay I03, now holds over a path extending through the upper No. 4 back contact of relay 220, lower No. 1 contact of relay IIlI, to ground on conductor 301. With relay 200 operated, relay Edi completes a circuit for relay I02 through the lower No. 2 contact of relay I0l, top back contact of relay to previously traced ground on brush 2 i6 and also for relay 302 over the top No. 1 front contact oi relay 2430, lower No. 2 contact of relay I0! to the aforetraced ground on brush HE. and 32, in operating, are provided with a hold-- ing circuit over the lower No. 2 contact of relay 302 to the back contact of relay 204 so that, when relay IOI releases at the the operator releases her ringing key, these relays hold up. With Relays I02 Lei accept the call.

"3H2 at the bottom No. 3 The ringing circuit to the called subscribers line other exchanges.

362, lower No. 2 back contact of relay 301, No. 2

.armature of relay 303 and thence either tobrush 312 or to brush 3 I 6. If ,now, the subscribers line is busy, ground on the sleeve lead will holdrelay 280 which, in turn, insures that relay I02 holds over the upper No. 2 front contact of .relay 208. Relay I02 gives supervision back to the operator since, when said relay operates, it reverses the talking conductors at the top and bottom outer contacts. The link is switched through to the busy line through the top No. 4 contact and the No. 1 bottom contact of relay 302, said circuit including the condenser 324. The operator can, therefore, talk to the subscriber and ask him to When both subscribers have cleared the line, ground is removed from the test lead of the called line and relay 20K! releases whereupon relay 192 is released, the line reversed and the operator given a clear signal. The operator then throws her ringing key which will cause the link to switch through to the required subscriber so that the call is completed with an additional set-up. Since relay .302 is still operatcd, ringing on the ring =sideof the line operates relay IOI, the upper No. 1 contacts of relay 362 'to the winding of relay IUI through condenser 13!. A circuit is now completed for relays 39! and 102 extending from ground on bank ll'l,

brush I I6, conductor I38, lower No. '3 contact of relay 3M, conductor I43, lower No. 2 contact of relay lfil, winding of relay IE2 to battery, and upper'No. 1 back contact of relay 2B0, lower No. 4 contact of relay 382, winding of relay '38! to battery. The operation of relay 3M releases'relay contact of relay 3M.

is then connected over a previously traced circuit from source of ringing current and upper winding of:relay 3!!!) and thence as previously traced over the subscribers loop back to resistance 322 and battery over the top, outer back contact of relay 300.

M uni-metering If thelink is used in a multi-fee metering area, terminal banks accessible to brushes M1 and 4538 of register switch 4 I G are used to give meter discriminations. The trunk groups reached byidigits 6, 7 and 8 are direct trunks to distant exchanges which are used for calls to these exchanges only. "I'hesmetering can, therefore; be determined com- .pletely by these digits.

In the case of the main exchange, however, calls can be set up to the main exchange and from thence to a number of If, for instance, the digit 0 is dialed, the operator will normally take care of -metering so that no automatic'met'ering is required. In the case of the digit 9, however,'the exchange to be reached may'not be determined until either the second, third, or fourth digit has been dialed. The register switch 4| 0 is arranged, therefore, so that if digit 6, 7 or'8 'is dialed, it

remains on the terminal to which it is driven and the number of metering impulses is determined by the connection from't'he meter pulse conductors l to 5 via the front contacts of the lower Nos. 1, 2 and 3 contact sets of relay "20'! to contacts 6, l and-8 on the terminal bank accessible to brush 408. It will be noted that the tenth contact of the bank accessible'tobrush 408 'is disconnected .on lower No. 1 front contact set of relay 201 so that, if 0 is dialed, there will be 'no automatic metering.

On the other hand a number of automatic exchanges may be reached via the parent exchange by dialing the digit 9 and the particular exchange to which connection is desired is then not known untila second digit is dialed. However, inasmuch'as the second digit is repeated to the distant exchange without registration on switch Q i [i, said switch can be given a second setting to correspond to the second digit by virtue of which setting the number of meter pulses can be determined. Further, the desired exchange may be reached only through another parent exchange which can be reached by direct switching from the first parent exchange by dialing a specific two digit code. But since the second parent exchange may itself be the center of a number of subsidiary exchanges, these latter exchanges may then be reached by dialing a third digit, in which event the number of meter pulses can be determined by a third setting of switch 423 made responsive by the impulses of the third digit. In

other words, the principle adopted for multi- .metering in this invention is the following: that if a certain digit is individual to an exchange it determines the exchange tariff and switch 416 remains on the trunk selected by the digit. If the digit is common to several exchanges a further digit is required to determine the tariff and switch 4H will be driven to a new home position after which it will accept another digit and thereby 'determine the tariif.

For the purpose of disclosing, and more completely understanding, this part of our invention we will describe the link multi-metering operations for (a) exchanges reached by single digit codes; (1)) exchanges reached by two digit codes; and (c) exchanges reached by three digit codes and (d) exchanges reached by four digit codes. It is understood, however,'that no limitation is intended by limiting the description or disclosure to three digit codes. The simple principle underlying the determination of the tariff by a digit individual toan exchange is capable of unlimited expansion to as many digits as may be required to reach an exchange and as such is included within the scope of the invention.

If the wanted exchange is selected by a single digit, say 7, and two meter impulses are required for a succesful connection to this exchange, then, at the end of this digit, the brushes of switch All] will be positioned on terminal '1 of their respective terminal banks as already described for a local call. When relay 3M releases at the end of the digit, relay )5 releases and disconnects the dial pulsing circuit from register magnet MI. The subsequent digits are now repeated to the distant exchange and the call completed in the same way as previously described for an automatic train reached through the main exchange by dialling 9. Now terminal 1 on the bank accessible to brush 458 is connected via the upper No. 2 back contact of relay M8 either directly to the No.2 pulsing conductor of the meter pulse control 'MPC or through the moving spring instance, a cam for each lead witl'i'battery con- V 7 change.

disengaged from the driving element.

. other suitable means and actuated by the closure of a starting circuit as, for instance, on start conductor 2I9. After one complete pulse cycle the cams may be prevented from any further rotation by the operation of a stop magnet over conductor 9 whereby the cam shaft drive is The magnetic drive or whatever suitable operating contrivance is used, must be so arranged as to operate from an external battery source so that, when started, a ground pulse is transmitted back over the starting conductor as a signal to the link to receive the forthcoming meter impulses.

When the called subscriber answers, relay H2 is operated over the called loop in the manner described and a circuit is completed tothe meter control circuit extending from battery through resistance 208, lower No. 3 contacts of relay 2I8, right contacts of relay 2I2, conductor 2I9, to ground through the starting mechanism of the motor control circuit. When the ground pulse is connected 'to conductor 2I9,.relay 204 is shortcircuited which, in releasing, causes the subscribers meter I44 to be connected to brush 408 over the following path: ground through the winding of the meter I44 and terminal on linefinder I20, brush I21, upper No. 3 contacts of relay 2I8, lower No. 2 contacts of relay H5, lower N o. 4 back contacts of relay 204, lower No. 2 front contacts of relay 304, brush 408, terminal 1, upper No. 2 back contacts of relay 4 I 8, upper No. 2 back contacts of relay 202, pulse conductor No. 2 to battery in the meter control circuit. The meter will now receive two pulses. a

At the end of the pulse cycle, the meter control circuit connects ground to the finish conductor 4 I 9 whereupon relay 2 I8 is short-circuited over the following path; ground on conductor 4 I 9, lower N0. 4 contacts of relay 2I8, upper No. 2

' back contacts of relay 204, resistance 2| I, thereby 'be reached by the automatic equipment at the main exchange and therefore have the digit 9 as the first digit. The second digit may be any other digit from 1 to '7, inclusive, and also 0. It is obvious from what has already been said in connection with reaching the automatic equipment by dialling digit 9, that said digit is used to select a trunk in the group extending between the calling exchange and the main exchange through the automatic equipment of which subsidiary exchanges may be reached by the dialling of another digit designating the desired subsidiary ex- Hence, the second digit is individual to the wanted exchange and by positioning switch 429 in accordance with the value of this digit the meter tariff for the exchange can be determined. That is, when digit 9 is dialled as a first digit it is necessary to restore switch 420 back to its home position after it has responded to said digit so that it can, on the second digit, .assume the position called for by the second digit individual to the called exchange.

At the end of digit 9, switch 420 is on terminal 9. The terminal accessible to brush 408 is strapped to the lower winding of relay I01. Hence, relay I01 operates over a circuit extending from battery through the lower winding of said relay, conductor I42, terminal 9. and brush 408, lower No. 2 contacts of relay 304, lower No. l front contacts of relay 204, lower No. 4 back contact of relay I08, lower No. 3 front contacts of relay 304,

conductor 348, lower No. 2 back contacts of relay I01, upper back contacts of relay 341, conductor 349, upper No. 3 back contacts of relay I06, con- 10 V driven to terminal I I over a circuit from battery through the winding of magnet MI and the interrupter contacts thereof, brush 495 and the 9th a terminal of the cooperating terminal bank, conductor M2 to ground on the upper outer front contacts of relay I01.

On the dialling of the next digit, which has been assumed to be 7, switch 420 is pulsed to 2!! terminal I8 over a previously described pulsing circuit and the position of the switch for the second digit determines the meter tariff for the two digit codes. At the end of the digit '7 relay 941 releases, accompanied by the release of relays I95 and I01. Subsequent digits will be repeated over the trunk in the manner already described but switch 420 will not respond to them since the stepping circuit is now disconnected by the release of relay I05, and the switch will remain on terminal I8.

Now terminals I 2 to I 8, and 2| on terminal bank of brushes 408 are reserved for codes 91? to 97 and 90 and these are two digit exchange codes requiring no further discrimination. These terminals, therefore, are strapped to the appropriate terminals on connecting block 4 I5 in accordance with the number of meter pulses required by each of the separate codes.

When the call is answered, metering occurs exactly as in the single digit code but the number of operations of the meter I44 depends on the meter pulse lead to which terminal I8 accessible to brush 408 is strapped.

Offices characterized by three digit codes are, in the present embodiment of the invention, those whose first two digits are 98 and 99. In such codes it becomes necessary, for tariff purposes, to reset switch. M0 in accordance with the value of the third digit of the code. This is done as follows:

Let it be assumed that "98 has been dialed. Then, according to operations already described, the brushes of switch 420 will be on the 19th terminal of their respective terminals. But inasso much as the 19th terminal accessible to brush 408 is connected to the upper winding of relay 4I8, this relay operates over a circuit completed from battery through the upper winding of said relay, 19th terminal and brush 4538, lower No. 2 front 5 contact of relay 394 and thence as previously traced to ground on conductor 301. Relay'4l8 operates and locks over its lower winding and lower No. 1 contact to ground on conductor 301 by way of the lower locking contact of relay 2I8. 7

It further extends its operating ground by way of its locking contact to conductor I 42 and thereby completes the circuit of relay I91 over its lower winding. Relay I01 operates, looks over its upper winding and lower No. 3 contacts over a prerelay I I5.

viously traced circuit and further holds relay I05 on its upper winding through said locking circuit. A self-interrupting circuit for magnet MM is now completed through battery, winding of said magnet, interrupter contacts, 19th terminal and brush 406, conductor M I, upper inner front contacts of relay I01, upper No. 2 front contacts of relay 30L to ground on the upper N0. 2 front contacts of Switch 420 is thereby driven to its home position and there awaits the dialing of the third digit of the code to which it Will respond since relay I05 is operated and the dial impulse circuit for operating magnet 4!, and previously traced, is now closed.

The impulses of the third digit will now be effective to advance the brushes of switch 410 to any one of their respective terminals I to I and since the terminals accessible to brush 400 are strapped to the terminal. block 4I5 according to the number of meter pulses required for each of the digits 1 to 10 the appropriate number of meter pulses will be transmitted at the time the charge is made for the call.

If it is assumed that the three digit code above considered is 986, then, after the third digit is dialed, the brushes of switch 4I0 will be on their respective terminals-6. When the digit has been received, relay 341 releases and, since relay I01 can no longer be operated through the 9th terminal accessible to brush 408, relay I releases and disconnects magnet 40I from the pulsing circuit. Subsequent digits will therefore not step switch M0 and when metering occurs as previously described, the tarifi will be determined by the strapping from terminal 6 accessible to brush 408.

It will be observed that terminals 6, 1 and 8 accesslble to brush 408 are connected to the upper moving springs I, 2 and 3 of relay M8 and that the respective cooperating back springs are connected to the terminals of block MS as required by the meter charges for the single digit offices 6, 1 and 8. On the other hand, the front contacts associated with the moving springs are connected to the terminal block 4 I 5 as required by the meter charges for three digit codes and particularly by the codes ending in 6, 7 and 8 In the case of single digit codes, relay M8 is not operated so that the back springs are efiective to give the required meter pulses while in the case of three digit codes relay 4 I8 is operated and if the third digit of the code happens to be a 6 or a 7 or an 8 the front spring of relay 4I8, making with the moving spring connected to the terminal marking the last digit of the code, will be effective to give the required meter pulses.

It will be further observed that meter pulse conductors 2, 3, 4 and 5 are carried through the back contacts of relay 202 which relay, it will be remembered, operates on calls from coin-box lines. The front contacts of the upper 2, 3, 4 and 5 armatures of relay 202 are, in turn, connected to the lower winding of relay 20I which is further connected to a terminal on block 4I5. This terminal is further strapped to all the terminals accessible to brush 408 representing codes which are not available to coin-box lines since the coinbox may not be arranged for variable collections as would have to be the case if calls were to be completed to oflices behind the single charge area. If, now, a coin-box subscriber does dial such an office relay 202 would operate as already described and a circuit would be completed from ground on brush 408, terminal on block 4I5 connecting with the lower winding of relay 20I to battery. Relay 20I would then operate and transmit NU tone to the subscriber, indicating to him that the office desired could only be reached by way of the operator at the main exchange.

If code 99 is dialed as the first two digits of 5 a three digit code, then after the dialing of the second 9, the brushes of switch 4-I0 will be their respective 20th terminal and of which that accessible to the brush 408 is strapped to discriminating relay 402. This relay, therefore, operates 10 in a circuit completed over its upper winding, 20th terminal and brush 408 to ground on relay i 55 as before traced and then looks over its lower winding and inner contact to ground on conductor w? via the lower locking contact of relay 2I8. Relay 492 further extends the operating ground through its upper contact to conductor I42 and thence to the lower winding of relay I01 which now operates and holds relay I05 in the same way as previously described for other three digit codes. As in the case of 98, the brushes of switch 4I'0 will now be driven to their respective home terminals after which magnet 40I will .respond to the impulses of the third digit. But

inasmuch as relay 402 is operated in this case, the meter pulses will be taken from the terminal on brush 401 to which it is driven by the impulses of the third digit. The first ten terminals accessible to brush 401 are strapped to the pulse conductors on block 4I5 in accordance to the number of pulses required to operate the subscribers meter for those three digit codes which have 9 as their middle digit.

The link circuit disclosed in Figs. 1 to 4 inclusive as an embodiment of this invention is arranged for metering offices designated by four digit codes and beginning with 998. If 998 is dialed switch 420 does not remain in position as described for 996 but drives to a new home position and accepts a fourth digit. At the end of the code 998, the brushes of switch 420 will be on terminal 8 and relay 402 will have been operated. Terminal 8, accessible to brush 401, is strapped to conductor I42 which connects with the lower winding of relay I01 and this relay 45 operates over circuit completed through brush 401 and terminal 0 cooperating therewith, lower front contacts of relay 402, lower No. 2 front contact of relay 304, lower No. 4 front contacts of relay 204, lower No. 4 contacts of relay I06, lower No. 3 front contacts of relay 304, conductor 348, lower No. 2 back contacts of relay I01, upper back contacts of relay 341, conductor 349, upper No. 3 back contacts of relay I06, conductor 301 to ground. Relay I01 operates, locks and holds relay I05 over a previously traced circuit whereupon switch M0 is driven to the 11th set of terminals. The next digit now influences magnet 40: since the impulse circuit is closed by the operation of relay E05 and the switch is driven to a set of terminals from I2 to 2| depending on the value of the digit. The terminals I2 to 2| accessible to brush 401 can, therefore, be strapped to pulse leads on block M5 to give correct tariffs for the exchange codes 9981 to 9980. Metering then takes place as before described.

Four digits local numbering When the rural automatic exchange is used in an area requiring four digits numbering, any suitable digit can be prefixed to the normal numbering and the register switch 4| 0 made to absorb this digit on calls to local subscribers. For instance, if the prefix digitis a 5; terminal 5 on the bankaccessible to brush 404 is wired to the wind- 

